America's top justices are considering what to do if they strike down the key provision of U.S. President Barack Obama's health care reform law.

The U.S. Supreme Court held its third and final day of arguments Wednesday on the law, examining whether parts of it should survive if the court determines the so-called "individual mandate" is unconstitutional.

The mandate requires Americans to purchase health insurance or face a financial penalty. But during Wednesday's arguments, Chief Justice John Roberts noted that many of the provisions "have nothing to do" with the mandate.

Conservative Justice Antonin Scalia said it was "totally unrealistic" to have the court go through all 2,700 pages of the legislation, saying "if you take the heart out of the statute, the statute is gone.'' Liberal Justices Sonia Sotomayor and Elena Kagan expressed skepticism that tossing out all of the provisions in the law was necessary.

Key aspects and programs of the Affordable Care Act:

Adult children can remain on their parent’s insurance coverage through the age of 26.

An end to lifetime limits on the dollar value of benefits available to people with serious medical conditions.

Business with more than 200 employees must enroll their employees in health insurance programs or pay a penalty.

Businesses with 50 to 200 employees who work 30 hours or more a week must offer insurance or money to workers who want to get insurance elsewhere.

Businesses with less than 50 employees are exempt from coverage provisions.

Who is Challenging the Law

Twenty-six U.S. states.

National Federation of Independent Business, an advocacy group for small business.

Several individuals.

Supporters say the individual mandate is needed to spread the cost of health care among all Americans, especially healthy people who might otherwise not purchase insurance, to cover more than 30 million uninsured people. But the 26 states challenging the law argue the requirement is an overreach of the federal government's constitutional powers. They say the law should be repealed in its entirety if the insurance mandate is found to be unconstitutional.

The Supreme Court's nine justices also spent time Wednesday listening to arguments on the law's expansion of the joint federal-state health insurance program for low-income Americans, known as Medicaid.

The court is expected to issue its decision in June.

The health care law is the most significant reform to the U.S. health care system in four decades. It bars insurance companies from denying coverage to people with pre-existing conditions or placing a cap on the benefits available to those with serious medical conditions. Many of the law's key provisions, including the individual mandate, do not take effect until 2014.

The case comes before a divided bench made up of five justices appointed by Republican presidents and four appointed by Democrats.

On Tuesday, the court's most conservative members, led by Justice Scalia, expressed doubt that the government can actually require people to purchase any type of product, including health insurance.

But Scalia's liberal counterpart, Justice Stephen Breyer, said the issue shows there is a "national problem that involves money, cost and insurance."

Both Chief Justice Roberts and Justice Anthony Kennedy also expressed concerns about the measure, but also seemed to acknowledge the need for the mandate in regulating the cost of health insurance.

The case before the nation's highest court represents a historic legal and political showdown about the Affordable Care Act, President Obama's signature domestic policy. Mr. Obama signed the bill into law two years ago despite objections by opposition Republicans.